Transience.

He who has attained to only some degree of freedom of mind cannot feel other than a wanderer on the earth – though not as a traveler to a final destination, for this destination does not exist.  But he will watch and observe and keep his eyes open to see what is really going in the world; for this reason he may not let his heart adhere too firmly to any individual thing; within him too there must be something wandering that takes pleasure in change and transience.

Friedrich Nietzsche